Printed circuit board assemblies are widely used in the manufacture of electrical devices, such as television receivers, video cassette recorders, computers and the like. The printed circuit board assemblies typically include a printed circuit board having a conductive printed circuit pattern formed on at least one of the surfaces of the board and various different types of electrical components which are mounted on the printed circuit board and electrically connected to the printed circuit pattern.
In the conventional method of manufacturing printed circuit board assemblies, the electrical components are initially positioned at precise locations on the printed circuit board so that the electrical leads of the electrical components are aligned with the appropriate contact pads of the printed circuit pattern. The electrical components are then mechanically secured in position. The electrical leads are then soldered to the contact pads of the printed circuit pattern.
The electrical components which are commonly employed in the manufacture of printed circuit board assemblies vary widely in size, weight, shape and function and require a variety of different mechanical fastening methods to secure the electrical components to the printed circuit board. Relatively small, lightweight leaded electronic components, such as axial leaded resistors and capacitors, can be secured to the printed circuit board by simply inserting the leads of the components through apertures formed in the printed circuit board and then bending the leads to mechanically lock the components in place. Other types of electronic components which generally are considerably larger and/or heavier in weight, such as transformers, motors, tuners and the like, must be more firmly secured to the printed circuit board. Still other types of components, such as speakers, certain types of heat sinks, daughter boards and the like, are required to be mounted so as to stand off from the surface of the printed circuit board. For both of the latter types of electrical components, it has become conventional practice to use mechanical supports which are secured to the printed circuit board to hold the electrical components in position.
In addition to the electrical components, printed circuit board assemblies also often include various types of mechanical devices, such as spacers, mounting brackets, reinforcement ribs and the like, which must likewise be secured to the printed circuit board at precise locations.
Because of the wide variation in the requirements for the mounting of different types of electrical components and different types of mechanical devices, a considerable number of different shaped parts are required to be secured in precisely determined locations on many types of printed circuit board assemblies.
In the conventional prior art method heretofore used in the manufacture of printed circuit board assemblies, the mechanical supports for the electrical components, mechanical devices and the like were initially formed from a molded plastic material or a metal stamping. After the required number and types of parts were prepared, the parts were secured in position on a printed circuit board. One method which was widely employed to secure the parts to the printed circuit board was to use metal fasteners, such as screws, to hold the parts in position. Another method which was also used was to mold the parts with spring-loaded leads, allowing the parts to be snap-fitted into preformed apertures in the printed circuit boards. The above-described methods had a number of distinct disadvantages. The parts required for the printed circuit board assemblies were made in a separate operation which inherently increases the expense and the lead time required for the manufacture of printed circuit board assemblies. Furthermore, because of the wide variety of different sizes, shapes and types of parts required for even a relatively simple printed circuit board assembly, a relatively large inventory of different types of parts had to be maintained which also significantly increases the overall manufacturing costs. A further related problem with the prior art methods was that a shortage of even one critical part could cause a disruption of the production of the entire printed circuit board assembly. A still further problem encountered when using metal fasteners to hold the parts in place was that metal fasteners would often become loosened from the parts on the printed circuit boards resulting in electrical shorts. The snap-in parts likewise were not satisfactory in that preformed apertures in the board had to be accurately formed in order for the part to be properly insertable and held in position on the printed circuit board. If the holes were slightly undersized, it was often difficult or impossible to insert the parts into the board. If the holes were slightly oversized, the parts would be loosely held and could even fall out of the board.
A still further problem encountered with the prior art methods was that numerous errors were made with regard to the specific types and the orientation of the parts in the printed circuit board. This was caused in some cases by human error during hand insertion of the numerous different types of parts into the printed circuit board. Even using automatic insertion equipment, defects in placement were often caused by malfunctions of the automatic insertion equipment due to variations in the exact shape of the parts being inserted. This problem was further complicated by the numerous and different types of parts required to be inserted at different specific locations in a typical printed circuit board.
It has also recently been suggested to mold a plastic board having the required supports and the like molded as part of the board and then thereafter apply the required circuitry to the board. This suggestion has not, however, proven to be satisfactory. The resulting three-dimensional boards are inherently expensive to manufacture and limited in size. It is, furthermore, extremely difficult to form the required electrical circuitry on the molded board with the supports and the like extending outwardly from the surface of the board.
The problems encountered with the prior art methods for making printed circuit board assemblies, as noted above, have become especially critical as a result of the increased need to automate as much as possible of the manufacture of printed circuit board assemblies. In order to realize the full benefits of automation, it is necessary that there be consistency from part to part employed in the automated assembly process to insure accurate placement with automated equipment. This is particularly true with regard to the printed circuit boards and the parts secured to the surface of the printed circuit boards as the automatic insertion of the electronic components associated with the parts on the printed circuit board requires that the proper type of parts be precisely located with the correct orientation to receive the electrical components.
It would be highly desirable if an efficient method could be provided for consistently manufacturing printed circuit board assemblies having the parts required for mounting electrical components and mechanical devices precisely located on the printed circuit board.